Such a coupling piece is known, e.g., from DE 298 11 460 U1. This coupling piece is a so-called midlock, which is used for lashing containers as deck cargo onboard ships, especially for joining two containers stacked one atop the other. The midlock is used whenever two 20-foot containers are placed on a space for a 40-foot container, namely at the container corner fittings on the front sides, facing one another, of the 20-foot containers, standing one behind the other. In fact, only a very narrow gap of about 76 mm is produced between the 20-foot containers standing one behind the other, such that the corner fittings arranged on these sides and therefore the midlock as well are poorly accessible for stevedores. The corner fittings are freely accessible on the other, free front sides. So-called twistlocks are generally used here, which are opened manually by the stevedore when unloading the container. The container is then raised, whereby the midlocks slide out of the corner fittings of the lower container because of the inclined standing of the container.
During the loading of the container, the midlocks are first suspended in the lower corner fitting of the upper container with the containers hovering over land. To this end, in older variants, hook-type catches were used on a front side (the side pointing in the longitudinal direction of the container to the front side of same) of the upper coupling projection. More contemporary variants, such as, for example, the midlock also illustrated in DE 298 11 460 U1, have lateral projections on the upper coupling projection that extend approximately in parallel to the stop plate. These projections grip into the lower corner fitting of the upper container. The opposite, lower coupling projection has a locking catch on a front side. When the upper container is placed on the lower container which is already located onboard the ship, either the entire midlock then slides against the upper container or the entire upper container slides forwards or backwards on a lower inclined surface of the locking catch and catches in the upper corner fitting of the lower container during the further lowering of the container.
This midlock has the following drawback. Usually onboard ships, the rear container corner fitting, into which a midlock is usually inserted, is poorly accessible, as explained above. However, there are also container ships, in which the containers are still accessible at least at some of the loading spaces, or because not all loading spaces are occupied, for attaching additional lashing means, for example, lock rods. However, in the prior-art midlocks, lashing means cannot be fastened in the upper corner fitting of the lower container, since the front-side opening is occupied because of the locking catch engaging therein. For this reason, a special hook fitting of a lock rod is suggested in DE 100 04 359 A1, which grips around the locking catch of conventional midlocks. Up to now, this hook fitting has not been used in practice.